Polymer composites containing a fluoropolymer and reinforcing fibres are known in the art. The fluoropolymer composites so obtained are advantageously endowed with good thermomechanical strength and chemical resistance to be suitably used in a variety of applications.
The coating of the fibres by the fluoropolymer matrix may be carried out according to various techniques, depending on the physical form of the matrix and of the fibres.
For instance, US 2010/0203328 (ARKEMA FRANCE) Aug. 12, 2010 discloses a process for impregnating continuous fibres comprising coating said fibres using a polymer matrix comprising at least one semicrystalline thermoplastic polymer having a glass transition temperature (Tg) less than or equal to 130° C. and nanotubes of at least one chemical element chosen from the elements from columns IIIa, IVa and Va of the Periodic Table. The coating of the fibres may be carried out according to a fluidized bed impregnation process, wherein the polymer matrix is in the powder form, or by passage of the fibres in an impregnating bath containing the polymer matrix in the melt state. As another variant, a film is prepared from the polymer matrix, especially by means of an extrusion or calendering process, then in placing it between two mats of fibres, the assembly being then hot-pressed in order to allow the impregnation of the fibres and the manufacture of the composite.
Also, U.S. Pat. No. 5,194,484 (E. I. DU PONT DE NEMOURS AND CO.) Mar. 16, 1993 discloses a process for making fluoropolymer composites comprising contacting a fibrous material with an aqueous fluoropolymer dispersion, precipitating the fluoropolymer from said dispersion to form a structure of fluoropolymer particles dispersed on said fibrous material, drying said structure and consolidating said structure by heating to a high enough temperature and applying sufficient pressure for a sufficient amount of time to form said structure into a solid shaped article.
In particular, poly(vinylidene fluoride) (PVDF) exhibits excellent toughness and corrosion resistance to severe environmental stresses, is thermally stable and resistant to creep at elevated temperatures and has a low permeability to gases and liquids, so that it offers great potential as a matrix for the development of fibre reinforced composites suitable for use in various applications including oil and gas applications.
However, dehydrofluorination of PVDF in the presence of strong bases represents one of the major issues encountered when compounding in the melt phase, under high pressures, fibres such as glass fibres with a vinylidene fluoride-based polymer matrix. When glass fibres are incorporated into said vinylidene fluoride-based polymer matrix by melt-processing techniques, more or less severe degradation of the vinylidene fluoride-based polymer takes place, depending on the composition of the glass, with formation of highly corrosive and highly toxic fumes of hydrogen fluoride.
There is thus still the need in the art for a process for impregnating a fibrous material enabling easy manufacture of vinylidene fluoride-based polymer composites and articles derived therefrom, said process providing fluoropolymer composites having high structural integrity and high adhesion at the fibre-fluoropolymer interface, while avoiding degradation phenomena adversely affecting the bulk properties of the fluoropolymer composites thereby provided.